This invention generally relates to a process and apparatus for the formation and development of electrophotographic images at low voltages. More specifically, the present invention is directed to a process and apparatus for the simultaneous charging, exposure, and development of imaging members, at low voltages; and wherein a high voltage corona charging device is not required. Accordingly with the improved process of the present invention, the use of devices, such as corotrons, which require high voltages of from about 3,000 to about 6,000 are eliminated and the attendant problems thereto are substantially reduced, including the undesirable emission of ozone. The process and apparatus of the present invention are useful in electrostatographic imaging systems, particularly xerographic imaging systems wherein a high voltage corotron device is not needed for charging, and developed images of high quality and excellent resolution are obtained.
The formation and development of electrostatic latent images is well known. In these systems generally, a corotron charging device, requiring from about 3,000 to about 6,000 volts is used to apply a charge density to a photoreceptor member. Subsequently, the photoreceptor imaging member is imagewise exposed, and the resulting latent electrostatic image is developed with toner particles. Thereafter the image is transferred to a suitable surface with a high voltage corotron charging device, followed by permanently fixing the image to a suitable substrate such as paper. Since the introduction of xerography many improvements have been affected in order to obtain high quality developed images while simultaneously improving the process conditions. However, a substantial number of these systems continue to require corona charging devices necessitating the need for costly high voltage power devices and the elimination of undesirable ozone generated by such devices.
There is disclosed in U.S. Pat. No. 2,968,552, a process wherein a layer of charged conductive toner particles are uniformly developed on an imaging member, such as a photoreceptor containing a transparent substrate. According to the disclosure of this patent, development is caused by an electrical bias from a development roll in the absence of photoreceptor charging. Subsequent to imagewise exposure through the transparent substrate of the photoreceptor device, paper is brought into contact with the toned photoreceptor causing toner particles to selectively transfer to the paper in the unexposed or imaged areas.
Additionally, there is disclosed in U.S. Pat. No. 4,014,697 a process for obtaining images by contacting a charge blocking surface present on a photoreceptor device, with a developer composition containing charged toner particles, providing an electric field of predetermined polarity between the photoreceptor and the transfer medium for uniformly attracting the toner particles to the photoreceptor surface, and subjecting the photoreceptor surface to activating radiation in image configuration for inducing an electrostatic charge pattern on the photoreceptor near the interface between the blocking layer and the developer material. An electric field is provided of an opposite polarity between the photoreceptor and the transfer medium for the purpose of transferring the toner particles in image configuration. Similar teachings are contained in U.S. Pat. Nos. 3,877,934 and 3,890,040. These patents thus describe a process in which simultaneous photoreceptor charging and exposure are obtained with an in-place developer composition. In these processes, the electric field applied across an electroded sandwich comprised of a photoreceptor and a toned donor is of one polarity during imagewise exposure and of the opposite polarity during image development. Upon separation of the toned donor from the photoreceptor member, imagewise deposition of toner particles on the photoreceptor occurs in the exposed areas.
Moreover, in U.S. Pat. No. 4,174,903 there is disclosed an electrophotographic printing device wherein a single processing station charges a photoconductive member in one mode, and develops an image recorded thereon in another mode. The electrically biased charging development unit useful in this process charges the photoconductive member by brush contact with conductive particles.
While the processes and apparatus disclosed in the prior art are suitable for their intended purposes, there continues to be a need for improved xerographic imaging processes and apparatuses. More specifically there continues to be a need for improved processes and apparatuses wherein images can be generated and developed without high voltage corona charging devices. Furthermore, there continues to be a need for processes wherein images can be generated and developed in a simple and economical manner, and the need for controlling effluents emitted by corotrons, are substantially eliminated. Furthermore there continues to be a need for processes and apparatuses wherein images obtained by the deposition of charged conductive toner particles on an imaging member, and imagewise exposure through a transparent substrate contained on the member, include the scavenging of toner particles for the purpose of improving background development. This scavenging is effected by removing toner particles from the photoreceptor in the unexposed areas prior to allowing the imagewise toner layer to contact the print supporting member. Moreover, there continues to be a need for improved processes for simultaneously charging imaging members, and exposing these members with an in-place developer composition consisting of conductive particles obtained with two component developer mixtures, or conductive single component toner particles. In this embodiment, the conductive toner particles provide an intimate electrode for the imaging member, thereby increasing the efficiency of photoreceptor charging by imagewise light exposure. Additionally, there continues to be a need for processes and apparatus wherein a photoconductive member can be simultaneously sensitized and developed with a single processing station, thus eliminating the need for repeated cycling of this member.